1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) display device, and more particularly, to a reliable organic EL display device in which occurrence of a dark spot caused by moisture is suppressed, and a method of manufacturing the same.
2. Description of the Related Art
In an organic EL display device, an organic EL layer is sandwiched between a pixel electrode (lower electrode) and an upper electrode, and, by applying a constant voltage to the upper electrode and a data signal voltage to the lower electrode, light emission of the organic EL layer is controlled, thereby forming an image. Supply of the data signal voltage to the lower electrode is carried out via a thin film transistor (TFT). Organic EL display devices are classified into a bottom emission type, in which light emitted from the organic EL layer is extracted toward a glass substrate which has the organic EL layer etc. formed thereon, and a top emission type, in which light emitted from the organic EL layer is extracted toward the opposite direction of the glass substrate which has the organic EL layer etc. formed thereon.
The light emitting property of an organic EL material used in the organic EL display device is degraded if moisture exists therein, and, when an operation is performed for a long period of time, the organic EL material becomes unable to emit light at a place where the light emitting property has been degraded due to the moisture. That place appears as a dark spot in a display region. This dark spot grows with time, and becomes a defect in an image. Note that a phenomenon called edge growth, in which a non-light emitting region increases around the periphery of a pixel, is also caused by the influence from moisture.
In order to prevent the occurrence or growth of a dark spot or the like, it is necessary to prevent ingress of moisture into the organic EL display device or to remove ingressed moisture. Accordingly, an element substrate having the organic EL layer formed thereon is sealed with a sealing substrate via sealing agents provided around the element substrate, thereby preventing moisture from ingressing into the organic EL display device from the outside. A space within the sealed portion is filled with an inert gas such as N2. On the other hand, in order to remove the moisture which has ingressed into the organic EL display device, a desiccant is provided within the organic EL display device. Such an organic EL display device is referred to as hollow sealing organic EL display device.
The hollow sealing organic EL display device has such problems as a difficulty in adjusting a gap between the element substrate and the sealing substrate, a difficulty in adjusting a pressure inside the sealed portion, contamination of the organic EL material due to a gas emitted from a sealing agent when sealing using the sealing agent, and low throughput.
As a measure for addressing the problems with the hollow sealing, there exists a technology in which the organic EL material is protected against moisture by means of a resin sheet which has a fixed film thickness and is sandwiched between the element substrate and the sealing substrate. This is referred to as solid sealing.
In JP 2004-139977 A, there is described an example of the solid sealing, and FIGS. 16A to 16D illustrate a configuration described in JP 2004-139977 A. Referring to FIGS. 16A to 16D, a photo-curing resin 120 formed on a film 110 having optical transparency is bonded, with the use of a pressure roller 105 which is heated up to 80° C., on an element substrate 10 provided with organic EL layers 22. Subsequently, by irradiating ultraviolet light, the photo-curing resin 120 is cured, and then, the film 110 having optical transparency is peeled off, thereby obtaining an organic EL display device which is sealed with the photo-curing resin. In addition, there is described a configuration in which the organic EL element is covered with a silicon nitride film if necessary.
In “Shinya Saeki, Nikkei Electronics, Sep. 10, 2007, No. 960, pp. 10-11”, as illustrated in FIGS. 17A to 17E, there is described a technology for sealing an organic EL display device as follows. Specifically, at a portion of a sealing substrate 40, which corresponds to an organic EL element 22, a resin film 107 is bonded, and then, a sealing agent 108 is printed around the resin film 107. The sealing substrate 40 having the resin films 107 and the sealing agents 108 formed thereon and an element substrate 10 having the organic EL elements 22 formed thereon are bonded together. Then, by irradiating ultraviolet light from the sealing substrate 40 side, a heating treatment at temperature of from 80° C. to 100° C. is performed, to thereby cure the sealing agent 108. At the same time, the resin film 107 which has started to have fluidity spreads across a space formed with the sealing substrate 40, the element substrate 10, and the sealing agent 108, and fills up the space. Lastly, the bonded substrates are divided into individual organic EL display panels as finished pieces.
In JP 2006-066364 A, there is described a configuration in which: a plurality of display elements are formed on a mother substrate; a sealing film is formed as a whole with respect to the plurality of display elements; and then, a protection film is removed from a terminal portion through laser ablation. FIGS. 18A and 18B illustrate the configuration described in JP 2006-066364 A, in which the plurality of display elements each including a light emitting portion 207 and terminal portions 209 are formed on a mother substrate 206, and are covered with a protection film 208. The protection film 208 is removed through laser ablation from parts 210 of each of the terminal portions 209, thereby forming opening portions 210.
With regard to the technology described in JP 2004-139977 A, there is described a configuration in which a resin sheet is bonded to individual organic EL display devices to protect the organic EL layer. However, there is no description or suggestion as to problems and the like which arise in a case where, with covering performed with the resin sheet, a plurality of organic EL panels are formed on a mother substrate and separated into individual pieces.
With the technology described in “Shinya Saeki, Nikkei Electronics, Sep. 10, 2007, No. 960, pp. 10-11”, it is necessary to achieve a balance in height between the resin film and the sealing agent, and, if an imbalance in height occurs, the lifetime of the organic EL display device is shortened. Further, with this technology, the resin film spreads, showing fluidity in a heating process after the sealing. As a result, however, a pressure within the organic EL display device is increased, and then, a leak path connecting to the outside is formed, posing a risk of shortening the lifetime of the organic EL display device. In addition, there is a risk of impairing the sealing performance due to the influence on the resin sheet from a gas emitted while the sealing agent is curing.
With the technology described in JP 2006-066364 A, after one resin sheet is bonded to the mother substrate having a plurality of organic EL display panels formed thereon, in order to remove the resin sheet for each of the terminals of the individual organic EL panels, processing is performed for the opening portions. As a result, the production capability becomes small. It is necessary to increase the number of facilities so as to increase the amount of production, which leads to an increase in production cost. Besides, for the ablation, a laser beam is employed at high energy, and hence there arises a problem of damaging a connection terminal. Further, in the removal using the laser beam, there is a fear that a residual resin sheet remains on the terminal.